Solid electrolyte fuel cells (hereafter referred to as fuel cells) are advantageous in that, for example, power can be generated at a high efficiency and waste heat can be used. For this reason, fuel cells have been developed. Such a fuel cell has, as a basic unit, a membrane electrode assembly (MEA) including a fuel electrode (anode), a solid oxide electrolyte, and an air electrode (cathode). The fuel cell further has a fuel-electrode collector disposed in contact with the fuel electrode of the MEA and a fuel-electrode channel that supplies a fuel gas such as hydrogen to the fuel electrode; and, similarly for the air electrode, which constitutes a pair together with the fuel electrode, the fuel cell has an air-electrode collector disposed in contact with the air electrode and an air channel that supplies the air to the air electrode. In general, the fuel-electrode collector and the air-electrode collector are conductive porous bodies through which a fuel gas or hydrogen and an oxidizing gas or air are passed. In other words, each electrode collector functions as a current collector and also serves as a gas channel. For this reason, the electrode collector primarily needs to have a high electric conductivity and not to increase the pressure drop of gas flow.
On the other hand, in order to cause an electrochemical reaction to proceed in a fuel cell at a reaction rate on the practical level, temperatures slightly higher than room temperature are not sufficient for the MEA, the fuel gas, and the like and heating with a heating device needs to be performed. In order to reduce the time for which protons H+ and the like generated during the electrochemical reaction travel through the solid electrolyte and in order to promote the electrochemical reaction itself, in general, the MEA and the like are set to a temperature of about 700° C. to about 900° C. Naturally, consumption of electric power for the heating results in a decrease in energy efficiency. In order to increase the rate of the electrochemical reaction, it is important that the gas introduced from the outside into the channel of the fuel cell reaches a temperature at a portion that is as near as possible to the inlet of the channel. For this reason, a process of preheating the gas is usually employed. In this case, the temperature of the inside (the MEA, the fuel-gas channel, and the like) of the fuel cell desirably reaches a predetermined temperature in a short time from the start-up of the fuel cell. In order to achieve such a temperature increase of the inside of the fuel cell in a short time from the start-up thereof, it is important to form the fuel-electrode collector and the like constituting the gas channels so as to have a high thermal conductivity.
As described above, a fuel cell is heated to a high temperature. For this reason, materials forming the fuel-electrode collector and the like need to have resistance to high-temperature oxidation and, in general, such materials are nickel (Ni) and the like. For the purpose of suppressing an increase in pressure drop and ensuring electric conductivity and thermal conductivity, examples of using Ni felt or Ni mesh as electrode collectors have been disclosed (Patent Literatures 1, 2, and 3). Another example of using a Ni-plating porous body or the like as a fuel-electrode collector has also been disclosed (Patent Literature 4).
Use of such a porous metal body can provide an electrode collector that satisfies some of the above-described properties.